1. Field of the Invention
The invention relates to a method for modifying the geometry of glass ceramics preferably locally, and to a glass ceramic with a local modification in geometry in the form of an elevation on the surface. The glass ceramic may comprise a layer on at least one surface.
Materials that are to be used include glass and glass ceramics (green glass state or already ceramized) that are preferably colored in the visible wavelength range (380 nm-780 nm) (and therefore usually materials that are also colored in the IR range). The modification in geometry is effected by local and time-limited exposure to electromagnetic radiation, such as e.g. laser radiation of a diode laser with a wavelength of 1 μm in CW mode and not strongly focused laser beam, preferably with a beam diameter of more than 400 μm.
2. Description of Related Art
A local change in the geometry of components made of glass ceramics is produced in three different ways according to the prior art:
First, a geometric increase can be achieved by attaching a second component to the actual component. Any joining process may be used for this purpose, such as brazing, welding and adhesive bonding. A drawback hereof is that in this case two components are required. Additionally, the joint is usually visually unattractive or forms a fracture starting edge. Moreover, it is difficult to add complex geometric elevations (circles, roundnesses, etc.) using an additional component.
Second, a local lowering in geometry can be achieved by (local) mechanical removal of material. Grinding and milling processes can be used for this purpose. The damage to the surface caused thereby may lead to a reduction in mechanical strength. Also, the modification of the surface in the abraded region (grinded or polished surface) may appear visually unattractive. Moreover, the generation of locally raised features is difficult in this way, since a lot of surrounding material would need to be removed to this end.
Third, WO 2012/134818 A1 describes a method according to which locally very limited color centers are produced in a highly transparent glass using an ultra short pulse laser in the UV range, which color centers then couple to the UV radiation better and better as a self-reinforcing effect, so that a heating effect is achieve which ultimately leads to a geometry change in the form of small, very localized elevations in the micrometer range.
A disadvantage hereof is the sophisticated ultrashort pulse laser which first has to establish the precondition so that the glass couples at all. Also, the self-reinforcing effect leads to uncontrolled heating and to an uncontrollable adjustment problem. A further disadvantage is that only glasses can be used which are sufficiently transparent in the UV range.